Tapered waveguide septum action is well known for its polarization selection characteristics. It would appear from simple inspection that the longer a tapered septum is made, the lower will be the discontinuity and better the bandwidth. In fact it has been found that there is an optimum taper and that increasing the length of the taper from optimum increases reflections and reduces bandwidth. Even with an optimum septum taper, reflections are not as low as desired and bandwidth is not as great as desired.